1. Field of the Invention
The present invention relates to a rotor for an electrical machine and particularly to a rotor for an EC motor with improved temperature stability, which is constructed in particular with NdFeB magnets, and to an electrical machine with such a rotor.
2. Description of the Prior Art
Electrical machines are known for instance in the form of electric motors, in which a ring magnet is secured to the rotor. In production, this necessitates securing the ring magnet to the rotor shaft. Typically, an adhesive is used for this. Often, the hollow-cylindrical ring magnets are also joined together with cylindrical carrier bodies (for a magnetic short circuit, often of steel) secured to the rotor shaft by means of applying adhesive in the gap between the ring magnet and the carrier body. In operation, however, because of the different coefficients of thermal expansion of the different materials for the ring magnet, the carrier body, and the adhesive, a relative motion of the components to one another occurs. Especially in the high temperature range, because of the different expansions of the materials, breakage of the ring magnet can occur. Another disadvantage of the adhesive process is putting the adhesive into the gap between the carrier body and the ring magnet. The gap must have a certain thickness, if the adhesive process is to be at all feasible in production. The greater the spacing between the ring magnet and the carrier body, however, the higher are the magnetic losses. Moreover, the attempt has been made for several years to use rare earths as the magnet material. That material, however, in comparison to the ferritic magnet materials, has even less expansion upon a temperature increase, to the point of negative expansion; thus if these materials are used, the risk of magnet breakage increases markedly.